Electric dental furnace



Allg 6 1940 B. FERON ELECTRIC DENTAL FURNACE Filed May l, 1939 Patented Aug. 6, 1940 i Y UNITED STATES PATENT OFFICE Application May 1, 1939, Serial No. 271,197

In Sweden November 20, 1937 1 Claim. (Cl. 21S-35) The present invention relates to dental furshaped resistance winding is preferably ten millinaces of the electric resistance type in which the meters and the length thereof ten meters. The resistance element or heating winding is wound ends of the resistance winding I are passed on to an exchangeable body or mufiie of fire-proof through .slots provided in the walls of the muiiie material, surrounded by an isolating muffle and 2, said ends being welded outside of the muifle 5 adapted to be introduced into the isolating mufle each to a connecting lug 3 or 4 respectively, said from the rear end thereof. lug preferably having a width of twenty milli- It is a general object of the invention to simmeters and a thickness of two millimeters. The

plify and improve the construction of dental furmuflle 2 carrying the resistance winding I and naces of this kind, in order to make the heating the connecting lugs 3 and 4 is removably in- 10 muiiie easily accessible for inspection and eX- Serted in a sleeve 5 of ireproof and preferably change in case of breakage or other disturbances ceramic material, said sleeve extending between caused by the intense heating of the muiiie and the front and rear walls 6 and l of the furnace. associated parts. Provided between the sleeve 5 and the side walls To this end the resistance winding of the heat- 8 and the bottom I8 of the furnace is heat in- 15 ing mufe is connected to the external connectsulating material 9. The furnace chamber I6 ing terminals through the medium of internal surrounded by the muie 2 is limited at its rear terminal contacts which according to the invenend by a lid I I of ceramic material, said lid being tion are placed inside the rear end portion of removably inserted in the rear end of the muiiie 2o the isolating muflie, but outside the space through and being provided with an opening for the in- 20 which the heating muflle is introduced into the sertion of a pyrometer B2 into the furnace chamisolating muffie. The internal terminals are ber. At the front the furnace chamber is limited adapted to be detachably connected to the resistby a door I3 adapted to close an opening proance windings by means of screws and connectvided in the front Wall of the furnace. The rear 5 ing lugs provided on the heating muie and are furnace wall 'I has an opening through which 25 accessible through an opening in the rear end the muiile 2 can be removed, said opening being Wall of the furnace, through which also the rear adapted to be closed with a detachable lid I4. ends of the muifles are accessible. Thus by re- Between the lid II forming the rear wall of the moving the cover, normally closing the opening, furnace chamber I0 and the lid i4 closing the access can be had to the interior of the mufes opening in the rear furnace wall there is formed 30 for inspection Without affecting the electrical a space I5 in which the connecting lugs 3 and 4 connections. If it is required to remove the heatof the resistance winding of the removable muffle ing mufle for repair or exchange this can be are connected to appertaining leading-in tereffected simply by unfastening the electrical conminals I6 or l'I, which are electrically connected 5 nections at the internal terminals and pulling with the current source. The space is normally 35 the heating muille out through the opening in filled by a removable filler body I9 of reproof the rear end wall of the furnace. material, such as steatite, a disk 2E) of asbestos The invention will now be described more in 01' other soft reproof material being preferably detail having reference to the drawing attached inserted between the filler body and the lid I4. to this specification and forming part thereof, in In the drawing the mufe 2 has been shown which as a one-piece body. Preferably, however, the

Figure 1 shows a vertical longitudinal section mufle is made in two semicylindrical halves fasthrough a dental furnace according to one emtened together by means of clay or the like, therebodiment of the invention, by' providing for straight joints which will crack Figure 2 shows the furnace according to Figin preference to the material of the muiile proper 45 ure 1 in front view, in case the stresses set up in the mule during Figure 3 is a cross section on the line 3 3 in heating ShOuld beCOme 1500 high- Figure 1, and The removal of a burnt-out mufe and inserting Figure 4 is a rear view of the furnace, of a new one is effected in the following manner.

Referring to the drawing, I designates the re- First the lid I4 at the rear of the furnace is re- 50 sistance element which has the form of a ribbon moved by loosening the four fastening screws of of resistance alloy wound spirally on the inside the lid. Thereafter the asbestor disk I9 and the of an open-ended sleeve-shaped body or muifle 2 ller body I8 are removed through the opening of fireproof material, such as steatite or other in the rear furnace wall, whereby access is had .55 ceramic material. The width of the ribbonto the connecting chamber. The pyrometer I2 55 is then pulled out, whereupon the lid il can be removed. After the connecting lugs 3 and have been disconnected from the terminals I6 and l1 the muiile 2 canbe pulled out through the opening in the rear furnace wall, whereupon a new mule with its appertaining heating winding can be inserted in position. The connecting lugs of the new heating Winding are then connected to the fixed terminals IB and il, the lid ll with the pyrometer l2 is inserted in the rear end of the sleeve-shaped' body or mufe, the ller'body i8 and the asbestos disk I9 are placed in position, and iinally the openingv in the rear wall of the furnace is closed by means of the lid IIL-whereupon the furnace is again ready for operation.

I claim:

An electric-resistanceA furnace comprising, a housing, a resistance Winding, an Outer muile of refractory material arranged in said housing,

an exchangeable inner muffie carrying the re sistance Winding and adapted to be inserted into the outer mule from the rear end thereof, a closure fitting the rear end of the inner munie, the end Wall of the housing having an opening therein for having access to the interior of the inner mule, the rear end Wall of the housing having an opening therein for having access to the rear ends of the muies, removable closures for said openings, Xed internal terminals accessible through the'opening in the rear wall and located in a free space inside the outer muiiie but outside of the space through which the inner mufe is introduced, c-onnecting lugs on the inner Inuiile, means for connecting said lugs to the internal terminals, and external connecting terminals electrically connected to said internal terminals and secured to the rhousing of the furnace.

BRJE FRON. 

